I don't get it.
According to message 2 the whammy it was an evil eye concept, which Al Capp 'took' and used. True a wham is a hit or strike. The baseball example suggests a 'bad luck' connotation.
No'vivid imagination' relevant, by the way.
In the TV programme I saw, it was a first hand narrative by the claimed user of the evil eye. A white American, he said he was a professional who was employed by boxers to be in their corner and put the whammy on their opposition. He explained that he would only use the single whammy, of course, except he then said, "And this is how I beat the Japs in World War two", and demonstrated the double whammy. He had learned how to do it from a black friend.
So this evidence for the term is claimed to go back to 1945 at least.